Tonight, as so many parents help their kids pack and get ready to head off to college, another family this evening remembering sending their son off. Disappearing just weeks later. And then, the gruesome discovery where he had been left. And his girlfriend talking with us about beingúyqñ trapped in a love triangle. Matt Gutman, with the case from the start. Reporter: It's a twisting obstacle course through swamp and thicket. Carlos Aguilar knows this rutted drive like a father knows the contours of his son's face. It's a route he's driven so many times -- leading to the site where the body of his teenage son, Christian, was discovered two years ago. The dirt track is getting narrower and narrower. It's amazing that anyone found this body. We've been following Carlos now for almost 30 minutes off of state road 24 in the wooded wastelands of north central Florida. The road is not that bad. Reporter: This road? Yeah. Reporter: No, it's not that bad. But it's not easy. Yeah. Now that you've seen this, you know that it was impossible for us -- even with 500 people -- to find him. Reporter: This hard working immigrant family from Colombia, plucking weeds and wetting the Earth with their tears. Considers this sacred ground. There's a cross with rosary beads, the name "Chris" is spray painted on a nearby rock. He's like a father's dream. Yes, the name of Christian means a gift from god. He was a gift from god. Reporter: You said that god has been with you through grief. He chooses this cross for me. Reporter: Life wasn't opposed to end here so soon for the 18-year-old scholar with the dancing eyes and the megawatt smile. What was your brother like? He was shy with people he didn't know, but once he got to know you, he would just open up. He would just start cracking jokes, start telling you things about himself, just, any way to get you to laugh. He would try to find a way. Reporter: So how did Christian Aguilar end up in this marshland, bound, face down in a shallow grave? What the cops call an "Enemy style" burial? This was some type of nefarious act, somebody was trying to conceal the body of a person. We find that most generally in cases of murder. Reporter: It's a story that made headlines up and down the Florida turnpike. A missing university of Florida student. Reporter: And got national attention. I still feel my son is still alive. In my heart. Reporter: The twisted murder mystery started at this elite charter school in Miami. Christian Aguilar was known for his easy-going cool, his charisma and his taste for hip-hop. So that's one thing that you and Christian had always shared is love of hip-hop and specifically Kanye? I mean, to this day I still love Kanye west so, yeah. We would just hop in his car, hang out for a while. Reporter: At the time, Erika friman was dating Christian's close friend, class clown, Pedro bravo. So tell me more about Pedro in high school. He was always quite sarcastic. Quite funny. He was able to make me laugh so easily. He was very much an animal lover and he liked action movies. You know, he liked superheroes. Reporter: The beauty with the big hazel eyes is the center of Pedro's world. We would go out. We would go on dates. We texted all the time. Reporter: Did you say you loved each other? Yes, we did. We did say we loved each other. And for a long time I thought that was kind of what love was like. Reporter: It seemed their love is built to last. I mean, not many relationships go almost three years, but -- Reporter: Especially not in high school. Yeah, it's, it's kind of unheard of. Reporter: They all go to prom together. But as graduation approaches, Pedro and Erika's puppy romance is almost over. At one point, you decided this relationship wasn't working for you. Yes, I did. I had talked to him about it, maybe we should go on a break. I don't think I'm happy. I felt like he almost manipulated me at that point of my life. Reporter: Erika breaks up with Pedro and abruptly the class clown's laughter is replaced with tears. He was very emotional about it. He was very, you know, he, he cried a lot. He was very, I mean, it was not what I was expecting at all when I broke up with him. Reporter: So when you broke up with Pedro, somewhere in your mind were you thinking, well, maybe I could start something with Christian? There was a little part of me that kind of hoped that, you know, Christian made me really happy and we had so many things in common, but a larger part of me was like, you know, it's never gonna happen. Reporter: She would leave Pedro behind to attend Santa Fe community college in Gainesville and study biology. Coincidentally, Christian is heading to Gainesville also, but to "The swamp," home of the Orange and blue -- the university of Florida gators. His future is full of promise. He has a scholarship, gets financial aid, and plans to study biomedical engineering. And when he and Erika run into each other in Gainesville, suddenly, sparks fly. It was crazy. We had these smiles on our faces from ear to ear and, I mean, we just looked at each other and like with these dumb faces, like, "Is this really happening?" Reporter: That sounds like true love in a way. I think we were soul mates. Reporter: Erika has moved on. Her ex has not, abandoning his plans to study engineering at a college in Miami and moving to Gainesville to enroll in Erika's college. When is the first time that you realize, "Oh man, Pedro's in Gainesville?" He actually sends me a text message. And I'm kind of thinking, how, this is, this doesn't sound Normal, you know? No one just packs up all their stuff and moves to a different city, you know, so far from their family for a girl. Reporter: No, it wasn't Normal. Neither was the journal Pedro kept. A brooding meditation on his quest to win Erika back. "No one will stop me," he wrote. "I will get out of Miami and into Gainesville, and I will get her back." I just was, kinda like, "Oh, my god, what are we going to do? Should we tell him? Should we not tell him? Or should we just live our lives and kind of -- if he sees us, or meets us or something, we will worry about it then." Reporter: "20/20" obtained that sketchbook and journal. It detailed his plan to get rid of acne, whiten his teeth and even wear a red shirt because he thinks it will be more eye-catching to the opposite sex. His hand written musings winding around seemingly unrelated sketches of cartoon characters, monsters, and sometimes sentimental doodlings. They almost looked like he could've been a cartoonist, you know? I mean, they were very beautiful pieces of art. Reporter: His drawings. What kind of drawings were they? I just saw, you know, pictures of hearts. There was captions next to the hearts. You know, there were broken hearts, and hearts in tiny pieces. Reporter: Adding insult to injury, Pedro now hears through the grapevine that his true love's heart now belongs to one of his best friends, Christian. The journal reveals his increasing anguish -- "I feel as if someone stabbed me and I bleeded out and died." "I want her back, please. I'll give anything." It's September 7th and this is the 34th street wall. Erika agrees to meet Pedro here. It's a place where for years U.F. Students have come to paint grafitti but this is an awkward moment at best because right away Pedro asks her if she's dating Christian. She says no. Reporter: He confronted you with the pictures of you and Christian. He showed me a picture of me standing next to Christian. And I was just like, "Listen, we're friends, you know, we're hanging out. You know, we're not dating, we're just hanging out." Reporter: But you lied to him. I did lie to him, yes. Reporter: Why did you lie? I just felt like it wasn't the appropriate time to tell him that. I don't want to push this kid at all, I don't want him to think anything, you know, that might throw him over the edge. Reporter: But Pedro is spinning out of control. He's even been talking suicide. And then, curiously, he calls Christian for help. Pedro calls Christian on a pay phone and he's like, I'm really depressed. And I was wondering if we can talk, you know, so maybe you can give me advice about how to deal with this, you know, depression. Reporter: Did he ask you if he should go, what you thought? We were a little concerned, that maybe he would try to fight him, or something of that sense, but you know, we talked about it, you know, you're going to meet on U.F. Campus. You're going to be fine. Reporter: They met at "The hub" -- the college bookstore here at the heart of this throbbing campus of the university of Florida. And what happens soon after will change three lives forever. I started calling him. I started texting him. He was not answering. I was like, well, I have to do something.

This transcript has been automatically generated and may not be 100% accurate.

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{"id":25094557,"title":"Teen Goes Missing After Meeting With Girlfriend's Ex","duration":"3:00","description":"Part 1: College freshman Christian Aguilar was last seen with his girlfriend's ex-boyfriend Pedro Bravo.","url":"/2020/video/teen-missing-meeting-girlfriends-25094557","section":"2020","mediaType":"Default"}